1. Field of the Invention
The present invention relates generally to the field of electrical lighting devices and, more specifically, to a portable task light which utilizes an array of light emitting devices such as light emitting diodes (LED's). The array of LEDs may be mounted on a printed circuit board disposed within a transparent or translucent tube.
2. Description of the Prior Art
There is often a need to enhance area illumination by using portable lighting products. The prior art devices used for this purpose include battery powered flashlights that have a limited life and a narrow focus; incandescent drop-lights that feature electrically inefficient, very hot and volatile tungsten filaments; and various types of fluorescent lights. Among the more popular light strips for a number of years have been of the fluorescent tube type strips which have found utility in a wide variety of applications. The fluorescent lighting strips also have disadvantages, however, in that a ballast must be included in the fixture. The ballast makes the light relatively large in size. More recently, various types of LED “strips” have been used as one type of array in endeavoring to provide an effective means to produce light with a minimum amount of heat. In certain of the prior art devices, an array of LED's is placed in various tubes or bulbs with reflectors for maximizing the light emitted. Standard light bulb bases have been used for connection to sockets and others have utilized couplings for attachment together forming a long lamp assembly.
There are a number of advantages to be obtained by providing a task or utility light in the form of a “strip” array which uses solid state LED's rather than a fluorescent tube and ballast. The use of LED's reduces power consumption to a bare minimum. Typical devices use on the order of 0.01 watts of power, making them extremely efficient. In determining the effectiveness of each type of illuminating device, a comparison is typically made of the efficiency of the light source in terms of the amount of light produced in relation to the amount of power consumed. This relationship can be used to calculate an “index” of relative efficiency. For general comparison, an incandescent light has an index of less than 24, a halogen lamp is only slightly better at 25, a mercury vapor is around 65 and a fluorescent lamp is in the neighborhood of 75, depending upon the type. By comparison, a light emitting diode (LED) in the T 1¾ style has a rating of almost 89.
Another advantage of the LED type strip lighting arrangement is that the LED strip is relatively cool to the touch. This allows LED type fixtures to be used in a host of user applications since they may be used safely around people and in close quarters. The LED type strip light also has a comparable useful life relative to other light sources. Yet another advantage of the LED type light strip is its small physical size. An LED arrangement can conveniently be packaged in the same or smaller size package as a fluorescent lamp with a comparable size bulb, since no ballast is required adjacent to the lamp. Further, since the light strip can use low voltage direct current power, the wiring is considerably smaller than that required in certain of the prior art devices.
LED strips also have the advantage of being extremely sturdy since the LED's are solidly mounted in a circuit board which in turn is held captive in a hollow thermoplastic tube This type of arrangement make the light extremely vibration and drop resistant. Further the tube can be plugged on each end as by end caps and sealed in such a manner as to make the invention waterproof for all practical purposes. These features make a strong and robust light strip compared to incandescent lamps that are subject to damage with vibration and fluorescent lamps that are fragile and often dangerous to handle.
Despite the various advantages offered by LED type light strips, various shortcomings remain. It would be advantageous to further reduce the size of the light assembly by eliminating the need for a transformer as a power source, either adjacent the strip or for placement on a wall near an electrical outlet.
Many of the prior art devices utilizing LED strips typically place the light sources side-by-side on a single plane or in various arrays that have failed to maximize the illuminative properties of the LED array. Prior art arrays generally are not adapted to varying their illumination patterns according to the target size or distance from the light source. In order to achieve the maximize beam disk flux efficiency at a selected task lamp distance.
The known prior art devices have also failed to take advantage of the benefits of driving the LED array with a pulsating direct current and have thus failed to maximize the LED intensity and the light output therefrom.